HTPC enthusiasts are often concerned about the quality of pictures output by the system. While this is a very subjective metric, we have decided to take as much of an objective approach as possible. Starting with the Core 100 review in 2010, we have been using the HQV 2.0 benchmark for this purpose.

The HQV 2.0 test suite consists of 39 different streams divided into 4 different classes. The playback device is assigned scores for each, depending on how well it plays the stream. Each test was repeated multiple times to ensure that the correct score was assigned. The scoring details are available in the testing guide on the HQV website.

In the table below, we indicate the maximum score possible for each test, and how much the Zotac GT 640 was able to get. As mentioned in the previous section, we used NVIDIA Graphics Driver v301.42 for the benchmarking.

HQV 2.0 Benchmark - Zotac GT 640

Test Class

Chapter

Tests

Max. Score

Zotac GT 640

Video Conversion

Video Resolution

Dial

5

5

Dial with Static Pattern

5

5

Gray Bars

5

5

Violin

5

5

Film Resolution

Stadium 2:2

5

5

Stadium 3:2

5

5

Overlay On Film

Horizontal Text Scroll

5

5

Vertical Text Scroll

5

3

Cadence Response Time

Transition to 3:2 Lock

5

5

Transition to 2:2 Lock

5

5

Multi-Cadence

2:2:2:4 24 FPS DVCam Video

5

5

2:3:3:2 24 FPS DVCam Video

5

5

3:2:3:2:2 24 FPS Vari-Speed

5

5

5:5 12 FPS Animation

5

5

6:4 12 FPS Animation

5

5

8:7 8 FPS Animation

5

5

Color Upsampling Errors

Interlace Chroma Problem (ICP)

5

5

Chroma Upsampling Error (CUE)

5

5

Noise and Artifact Reduction

Random Noise

SailBoat

5

5

Flower

5

5

Sunrise

5

5

Harbour Night

5

5

Compression Artifacts

Scrolling Text

5

5

Roller Coaster

5

5

Ferris Wheel

5

5

Bridge Traffic

5

5

Upscaled Compression Artifacts

Text Pattern

5

3

Roller Coaster

5

3

Ferris Wheel

5

3

Bridge Traffic

5

3

Image Scaling and Enhancements

Scaling and Filtering

Luminance Frequency Bands

5

5

Chrominance Frequency Bands

5

5

Vanishing Text

5

5

Resolution Enhancement

Brook, Mountain, Flower, Hair, Wood

15

15

Video Conversion

Contrast Enhancement

Theme Park

5

2

Driftwood

5

2

Beach at Dusk

5

2

White and Black Cats

5

2

Skin Tone Correction

Skin Tones

10

0

Total Score

210

178

We find that score closely tracks what we had for the GT 540M in the ASRock Vision 3D 252B review. In fact, the only difference is the fact that the horizontal scroll response time has been improved a bit, enabling it to score two more points in that test. Given that the GT 540M had no trouble deinterlacing 1080i60 content, it was not a surprise to find that the GT 640 sailed through those tests. In the next section, we will look at some rendering benchmarks to see how deinterlacing operations load up the GPU. Chroma upsampling algorithms are passable, and there is no difference in quality between what was obtained through the 540M and what we got with the GT 640.

In our review of the video post processing features of the GT 540M, we had indicated that the contrast enhancement and skin tone correction features didn't work. We found no change in the v301.42 drivers. However, we did find contrast enhancement working with the black level testing clip in the AVS HD 709 calibration suite. This just proves that the dynamic contrast enhancement feature in the NVIDIA drivers doesn't work as effectively as Intel's or AMD's.

Should the low HQV score or lack of proper dynamic contrast enhancement prevent you from choosing the GT 640 for your HTPC? Definitely not! The nice aspect about NVIDIA GPUs is the fact that there are lots of HTPC software packages available to take advantage of the GPU resources. As long as the hardware deinterlacer works (it does, as the HQV scores for those tests indicate), and there are enough shaders and other computing resources available to let madVR work its magic, the HTPC end-user has no reason to worry. Advanced HTPC users tend to distrust any post processing done by the drivers, and would rather not let the driver mess with the video output by applying its custom post processing algorithms (which tend to break with every new driver release).

However, video post processing algorithms are not the only issue-prone HTPC aspects in the driver. Proper black levels are necessary irrespective of the color space being output. The gallery below shows that the behavior of the driver doesn't correlate in any way to the settings in the control panel. NVIDIA drivers seem to adopt two modes for the limited (16-235) and full (0-255) settings, one for global (desktop, photos etc.) and one for videos. Global mode is chosen to be limited (16-235) for all in-built resolutions and full (0-255) for all custom resolutions when in YCbCr mode with no way to change this (the gallery below shows correct dynamic range being chosen in RGB mode for still photos / desktop). The dynamic range for video and desktops are also different. Toggling the dynamic contrast enhancement box also seems to affect this setting. In addition, there is no way to specifically choose RGB Full or RGB Limited in the current drivers.

This dynamic range issue was apparently present in the Vista days, and fixed earlier. There appears to be a regression in the state of this bug recently, and we have been observing problems since May 2011 at least. A method to fix the issue has been outlined on Microsoft's official Windows community forums. It is disappointing to note that NVIDIA has still not fixed the issue despite the bug being a major annoyance for many HTPC users.

There's no reason this wouldn't be similar in speed to a GTX460 if it had DDR5. The only difference would be 128-bit vs 192-bit memory bus, everything else would be an advantage: same number cores, substantially higher clock speed, lower power consumption increasing overclocking headroom, etc.Reply

You forget: substantially lower shader clock speed, more coarse shader grouping -> more difficult to use them all at once, and software scheduling -> need a better compiler, can't do runtime optimizations.Reply